1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device such as a metal oxide semiconductor (MOS) device enabling the effect for gettering of impurities from a semiconductor substrate.
2. Description of the Related Art
In general, a MOS structure is obtained by forming a gate insulating layer and a gate electrode on a semiconductor substrate. In order to reduce a fluctuation in threshold voltage of the MOS structure, a diffusion and oxidation process is carried out for gettering impurities from the semiconductor substrate. In this diffusion and oxidation process, an oxidation layer made of silicon dioxide is formed on the semiconductor substrate and the gate electrode.
In the above-mentioned diffusion and oxidation process, however, the oxidation layer is also grown between the semiconductor substrate and the gate electrode, and as a result, the edge of the gate electrode is deformed, i.e., warped, which will be explained later in detail. This warped edge of the gate electrode fluctuates the threshold voltage of the MOS structure i.e., deteriorates the characteristic of threshold voltage of the MOS structure.